The present invention relates to a laser gradient setting device for setting reference lines in civil engineering works.
In civil engineering works, it is necessary to have a horizontal reference line or a reference line tilted at a given angle with respect to horizontal line. A laser gradient setting device is used for setting such reference lines.
For example, in case concrete pipes are laid for sewage construction, the pipes must be laid without bending and must be tilted at a given angle.
As typical working processes to bury and lay concrete pipes, and so on in soil, there are the working processes to excavate the ground, to lay concrete pipes one after another into the excavated ditch, and to bury them.
For each given linear section, the ground is excavated to a depth deeper than the depth where concrete pipes are to be laid, and concrete pipes are laid on a temporary base at the bottom of the ditch.
These concrete pipes are used as a flow passage for city water, sewage or other liquid, and these are laid at a given inclination and without bending. If the buried concrete pipes are twisted or turned upward, downward, leftward or rightward, the liquid is stagnated, stopped or leaks out into soil, thus being unable to fulfill the function as a flow passage. Therefore, a proper reference line must be set when concrete pipes are to be installed.
A laser beam is suitable for providing such a reference line because it has not become slack (as thread does when it is used over a long distance) and because it causes no disturbance during work and it is not cut off due to interference with concrete pipe or working personnel.
The laser gradient setting device is used for setting a reference line when concrete pipes are installed.
Description is now given of a conventional type laser gradient setting device in connection with FIGS. 5 and 6.
A conventional type laser gradient setting device 1 in horizontal installment emits a laser beam, which provides a reference line in horizontal direction. If the laser beam is aligned with horizontal line, it provides a horizontal reference line. If the laser beam is tilted at a given angle, it gives a reference line with a gradient.
For each given linear section, a vertical hole 3 deeper than the depth at which the concrete pipe is to be laid is excavated at a starting point to bury the concrete pipe 2, and a burying ditch 4 continuous to the vertical hole 3 excavated at a depth deeper than the depth where the concrete pipe is laid. The laser gradient setting device 1 is installed in the vertical hole 3. A laser beam is emitted at a gradient .theta., and a reference laser beam L is provided. The concrete pipe 2 is laid in the burying ditch 4 via a temporary base 5 in such manner that its axis corresponds with the reference laser beam L.
When the axis of the concrete pipe 2 corresponds with the reference laser beam L, the concrete pipe 2 is buried by filling the burying ditch 4.
The laser gradient setting device 1 must be installed accurately in horizontal position when it is initially installed. In the past, it has been customary to install the laser gradient setting device 1 in horizontal position as follows: A support 6 is provided above the vertical hole 3, and a transit 7 is placed on the support 6. A plumb bob 8 is suspended from the transit 7 to set a known point 10. Further, the laser gradient setting device is installed in the vertical hole 3, and the plumb bob 8 is aligned with the center of the laser gradient setting device. Then, the plumb bob 9 is suspended from the laser gradient setting device 1 to align the plumb bob 9 with the known point 10.
In the conventional positioning method to use the plumb bob, there must be two workers to position the plumb bob, to stop swinging of the plumb bob and to adjust thread length, and adjustment must be repeated in order to accurately align the plumb bob from the transit and the plumb bob from the laser gradient setting device with each reference point. This means low working efficiency and very complicated working procedure. The above adjustment must be repeated when deviation occurs due to vibration caused by passing vehicles during work or when the work is resumed after temporary interruption, or when regular checking is performed. Thus, much time is required for such adjustment.